Galaxy’s cloud catalog reveals hydrogen fog

About half of the Whirlpool galaxy's hydrogen molecules (blue) fill the spiral in a foglike layer, not in giant, individual clouds where stars form. The finding that has implications for understanding how new stars form.

A fog of hydrogen molecules — a raw ingredient for making baby stars — fills the Whirlpool galaxy.

Astronomers thought most of this form of hydrogen gas would exist in giant clouds of molecules that nurture the birth of new stars. But detailed radio telescope observations cataloging the clouds of the Whirlpool galaxy, or M51, suggest that almost 50 percent of the molecular hydrogen exists in a gas layer that spreads throughout the spiral and envelopes the clouds instead, researchers report in the Dec. 10 Astrophysical Journal.

The galaxy sits about 23 million light-years from Earth in the constellation Canes Venatici. Additional observations of its spiral arms suggest that the pressure the molecular hydrogen fog exerts on the giant clouds plays a larger role in making new stars than previously thought, the astronomers argue. It is also not yet clear whether similar molecular hydrogen layers exist in other galaxies.